Kategorie: ‘Publication’
New publication:
Gentle dissolution of chitosan
Despite its very low pKa value, hydrochloric acid is one of the most commonly used acids in the production of chitosan hydrogels for biomedical applications. Although hydrochloric acid is widely used, the occurrence of unwanted depolymerisation in the production of hydrogels from chitosan hydrogels is often disregarded. In order to fully exploit the potential of chitosan as a renewable resource, a new, very mild method for the preparation of chitosan solutions is described here.
These solutions dry to clear, transparent films that remain completely water soluble and absorb up to 70 wt% water from the water in the 90 % RH vapour phase at 25 °C. Absorption follows simple first-order kinetics and the rate constants The rate constants increase with increasing humidity up to about 71 % RH, where a metastable chitosan trihydrate salt appears to be formed. Desorption is slightly faster, but more complex, as it involves two different first-order processes. In addition, the films produced in this way are thermally more stable than the usual chitosan hydrochloride.
M. B. Endres, O. Weichold
Sorption-active transparent films based on chitosan
Carbohydrate Polym. 2019, 208, 108–114. https://doi.org/10.1016/j.carbpol.2018.12.031
New Publication:Innovative Hydrogel Solutions for Sustainable Concrete Re-Alkalisation
A recent publication in Soft Matter (Issue 40, 2018) introduces a novel highly alkaline hydrogel designed to restore the alkaline buffer capacity in carbonated cementitious materials. This property is essential for preventing steel corrosion in reinforced concrete.
The hydrogel is based on a copolymer of diallyldimethylammonium hydroxide (DADMAOH) and methacrylamide. The addition of methacrylamide as a co-neutral monomer allows for extensive tunability of the gel’s rheological properties. The viscosity increases a thousandfold—from 0.35 Pa s to over 350 Pa s—when 10 mol% methacrylamide is used, showcasing the material’s adaptability.
- Ion Exchange: Experiments demonstrated efficient diffusion of hydroxide ions from the hydrogel into carbonated material, accompanied by the release of carbonate ions.
- Re-Alkalisation: The gel’s effectiveness was confirmed through the phenolphthalein test (DIN EN 14630:2007-01) and IR spectroscopy.
- Universal Applicability: The gel can be applied both for modern infrastructure maintenance and the preservation of historical monuments.
Jung, A.; Weichold, O.
Preparation and characterisation of highly alkaline hydrogels for the re-alkalisation of carbonated cementitious materials
Soft Matter 2018, 14 (40), 8105–8111. https://doi.org/10.1039/c8sm01158c.
New publication
Corrosion current drives corrosion sensor
New corrosion sensor for reinforced concrete requires no external power source. Steel corrosion causes enormous economic damage every year, which could be reduced by installing suitable monitoring devices. These should be simple, reliable and durable and should not require any maintenance or servicing. The present electrochromic device is designed to use the macrocell current of an active, chloride-induced corrosion element as an energy source to trigger a colour change. In this way, the system remains inactive until corrosion occurs. The device consists of diheptyl viologen in a liquid polymer electrolyte of LiClO4 and poly(ethylene glycol). The addition of viologen lowers the resistance but does not cause any further changes in the electrochemical properties of the polymer electrolyte. The impedance spectra indicate that ion transport rather than capacitive effects dominate the electrochemical properties. Experiments with direct current in the μA range show electrochromic switching times of several minutes, which is sufficient for the intended monitoring application.
T. Juraschek, O. Weichold
Development of an electrochromic device triggered by the macrocell current in chloride‐induced corrosion of steel‐reinforced concrete
J. Phys. Org. Chem. 2017, e3739. https://doi.org/10.1002/poc.3739
New Publication:Silane-Based Water Repellents
Together with co-author J. P. Lecomte, Prof. Dr. Oliver Weichold contributed the chapter Silane-based Water Repellents for Inorganic Construction Materials in the book Silicone Dispersions (2016).
This chapter explores the use of silane-based water repellents specifically designed to protect inorganic construction materials such as concrete and cement. Moisture and its resulting damages pose significant challenges to the durability of structures. Silanes and siloxanes, as organic compounds, counteract this issue by penetrating deeply into porous materials and creating hydrophobic properties.
The authors demonstrate how these technologies help mitigate damage from freeze-thaw cycles, chemical attacks, or reinforcement steel corrosion without compromising the breathability of the materials. In light of global challenges such as limited raw material availability and increasing sustainability requirements, extending the service life of structures is of paramount importance.
Weichold, O.; Lecomte, J.P.
Silane-Based Water Repellents for Inorganic Construction Materials
CRC Press: Boca Raton, FL, USA, 2016;Volume 10 10.1201/9781315371177-11
New publication
Structure formation in oligomers
How can the thermal stability and crystallinity of oligomers be controlled? Four members of a homologous series of chlorinated poly(vinyl ester) oligomers from poly(vinyl acetate) to poly(vinyl stearate) with degrees of polymerisation of 10 and 20 were prepared by telomerisation with carbon tetrachloride. All oligomers are thermally degraded in two main steps, whereby HCl and side chains are lost before the backbone is degraded. The polymers with short side chains, up to poly(vinyl octanoate), are amorphous and show internal plastification, while those with long side chains are semi-crystalline due to side chain crystallisation. The glass transition and melting temperatures as well as the initial decomposition temperature are more strongly influenced by the side chain length than by the degree of polymerisation. Thermal stability is improved when both the size and the number of side chains increase, but only long side chains lead to a significant increase in decomposition resistance.
D. Heinze, T. Mang, C. Popescu, O. Weichold
Effect of side chain length and degree of polymerization on thedecomposition and crystallization behaviour of chlorinated poly(vinylester) oligomers
Thermochimica Acta 2016, 637, 143-153. http://dx.doi.org/10.1016/j.tca.2016.05.015
New publication
Poly(vinyl acetate) plasticises itself
No additional plasticiser required. Poly(vinyl acetate), PVAc, with a degree of polymerisation Xn≈10 was produced by free radical chain transfer polymerisation with carbon tetrachloride and used as an oligomeric plasticiser for commercial PVAc. After H/Cl exchange at the chain ends, the product exhibits high thermal stability and excellent melt compounding properties. Blends of oligomeric and commercial PVAc show simple glass transition temperatures, which decrease with higher oligomer content, and exhibit small negative deviations from Fox’s linear additivity rule. This suggests that plasticisation and miscibility are mainly due to entropic effects. Injection moulded thick specimens show ductile behaviour at oligomer contents >10 wt%, while sheets with a thickness of 0.2-0.5 mm appear flexible already at 7.5 wt%. The oxygen permeability coefficients are an order of magnitude lower than those of low-density polyethylene. Due to the sum of their properties, the plasticised sheets represent a promising alternative for the production of barrier materials.
D. Heinze, T. Mang, K. Peter, M. Möller, O. Weichold
Synthesis of Low Molecular Weight Poly(vinyl acetate) and Its Application as Plasticizer
J. Appl. Polym. Sci. 2014, 40226. https://doi.org/10.1002/APP.40226
